This invention relates to a magnetic recording medium conveniently employed as a magnetic tape for recording/reproduction of short wavelength signals, such as a magnetic tape for a so-called high-band 8 mm magnetic video tape or a magnetic tape for a digital video tape recorder (VTR).
Up to now, a coated magnetic recording medium, in which a magnetic paint is coated on a non-magnetic support and dried to form a magnetic layer, has been widely employed as a magnetic recording medium. The magnetic paint is comprised of a powdered magnetic material, such as magnetic powders of oxides or alloys, dispersed in an organic binder, such as a vinyl chloride- vinyl acetate copolymer, polyester resin, urethane resin or a polyurethane resin.
On the other hand, in keeping up with the demand for high-density magnetic recording, a so-called magnetic metal thin film type magnetic recording medium, in which a magnetic layer is formed by directly depositing a magnetic metal material, such as a Co-Ni alloy, a Co-Cr alloy or Co-O, on a non-magnetic support, such as a polyester film, polyamide film or a polyimide film, by plating or a vacuum thin film forming technique, such as vacuum deposition, sputtering or ion plating, has been proposed, and is attracting attention.
The magnetic metal thin film type magnetic recording medium has a number of merits. That is, such recording medium is not only superior in coercivity, but also may,have an extremely small thickness of the magnetic layer thus resulting in extremely low thickness loss during playback or recording demagnetization. In addition, there is no necessity of mixing a binder, a non-magnetic material, into the magnetic layer, resulting in the increased packing density of the magnetic material.
Above all, an obliquely deposited magnetic recording medium, in which the magnetic metal material is vapor-deposited in an oblique direction, is being put to practical utilization, since it is superior in electro-magnetic conversion characteristics and capable of producing a larger output.
These recording media may be in the shape of a disc or a tape depending on the type of the recording/reproducing apparatus employed. If the recording medium is tape-shaped, a back coating layer formed of non-magnetic pigment powders and a binder is usually provided on the surface of the non-magnetic support opposite to the tape surface carrying the magnetic metal thin film for improving sliding properties relative to sliding members, such as guide pins, as well as for assuring good running properties.
In the field of magnetic recording, the tendency is towards a small size of the recording/reproducing apparatus, and towards the reduction in size of a tape cassette as a recording medium. In keeping up with such tendency, there is also a demand for increasing the amount of the information that can be stored in a tape cassette. For meeting these demands simultaneously, it is necessary that a magnetic tape as long as possible in length be accommodated in a small size cassette.
Thus, in order to reduce the volume taken up by a tape roll in a tape cassette, a magnetic tape with a further reduced thickness is desired. With the conventional magnetic tape, although the magnetic layer may be significantly reduced in thickness by employing a magnetic metal thin film, the back coating layer on the opposite side thereof is still thick, so that there is ample room for improvement.
However, if the back coating layer is to be reduced in thickness, with its composition remaining unchanged, the surface resistance is increased, while jitter or electrical discharge during tape running is induced, thus interfering with stable tape running performance.